We are studying the modulation of the expression of the gal operon of E. coli. We have so far shown that the operon is controlled by two promoters, which are modulated by cyclic AMP in opposite ways. Both the promoters are under the negative regulation by the gal repressor. The repressor inhibits transcription by binding to two operator sites. One is located at a more conventional position, i.e., near the promoter and the other at an extraordinary position, i.e., within the first structural gene. In order to study the interaction between the gal repressor protein and the two operator DNA elements, we have cloned the repressor gene into a maximum expression vector and have purified the protein. We have also cloned the two wild type and mutant operator elements needed for the repressor binding studies.